Inconsistent Verifier Results: Defects

Barcode on white surface

We were recently invited to a flexo printer who was getting inconsistent verifier results. The barcode was a UPC on a clear poly bag. When the symbols were tested on the flat, white substrate in the light box, they graded much worse than if the operator held the barcodes in the palm of his hand. Why the inconsistency–which grade to believe?

Barcode held in hand

Upon close examination it was revealed that the symbols were heavily over-printed and showed defects within the bars and haloing at the edges.
The white substrate accentuates the defects and caused downgrading of the ISO parameter Defects. The defects were less obvious when the symbols are verified in the user’s hand.

Which test should the printer believe? The inconsistent verifier results are caused by defects in the barcode, so the question is not “which test to believe” but “why are they so different?” If these barcodes fail to scan at point of sale, the brand owner will undoubtedly question why the printer “optimized” the verification reports.  The mystery will then be solved and that decision will no longer seem like a good one.

GS1 recommends that verification should take place with the barcode in its final form. That of course was impossible for this printer and probably for most CPG printers. It is likely that the performance of a UPC symbol on a clear plastic bag would be influenced by the color or texture of the product in the bag, which becomes the background for the barcode. But it is impractical at best for a food product bag printer to have samples of packaging contents on site; GS1’s recommended verification procedure must take place later.

But after many thousands of bags are printed it is too late to make design changes. A wise brand owner would insist on an opaque, highly reflective background behind the barcode to minimize the effects of product in the container on barcode performance. An even wiser brand owner would put somebody on the printing floor with product sample and a verifier just to make sure the design accommodations are working as intended.